Since an organic light emitting diode directly emits light from an emission layer positioned between a cathode and an anode, there is an advantage in that a backlight is not required, an expression range of light is wider than that of a Liquid Crystal Display (LCD), and a black level is excellent. That is, in the organic light emitting diode, when a voltage is applied to the cathode and the anode, electrons and holes are injected into each electrode and the injected electrons and holes pass through an electron transport layer and a hole transport layer, respectively, to be coupled to each other in the emission layer.
A light emitting material of the emission layer is excited by energy due to the coupling and the light is generated when the light emitting material returns from the excited state to a ground state again. The light generated when the light emitting material returns from the excited state (singlet state) to the ground state as it is fluorescence, and the light used when the light emitting material returns from the singlet state to the ground state via a triplet state having a slight low energy level is phosphorescence. In spite of the excited state, energy that is not properly used with the light may be inactivated without being emitted.
In the organic light emitting diode, as the cathode, a metal thin film such as aluminum and silver/magnesium alloys, calcium, and the like, and as the anode, a transparent metal thin film such as indium tin oxide called ITO may be used. An organic compound layer formed between the cathode and the anode may include a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), and an electron injection layer (EIL). When a driving voltage is applied between the cathode and the anode, the holes passing through the HTL and the electrons passing through the ETL are moved to the EML to form excitons, and as a result, the EML generates visible light. The generated light is reflected on a reflective surface and transmits a transparent electrode and a substrate (a glass plate, a plastic plate, or the like).
The organic light emitting diode may be classified into a passive matrix organic light emitting diode (PMOLED) and an active matrix organic light emitting diode (AMOLED) according to a control mode thereof.
The PMOLED has a structure in which a voltage is applied to each of a horizontal axis and a vertical axis of a light emitting element which is disposed on a screen, respectively, to illuminate a cross point thereof, and thus, the structure is relatively simple and production cost is low, but there is a disadvantage in that a delicate screen cannot be implemented. The AMOLED is intended to overcome the disadvantage of the PMOLED and has an advantage that a thin film transistor (TFT) is embedded for each light emitting element to control whether each element emits the light, respectively, and recently, since a screen size thereof may be applied to a large device, an application range thereof is widened.
In Korean Patent Registration No. 10-1170806, a device for a passive matrix is described, but particularly, a method for implementing a touch function in the PMOLED is not described.